Rheostat.



No. 704,448. Patented July 8, I902.

A. C. EASTWOOD.

RHEOSTAT.

(Application filed Apr. 10, 1902.)

(No Model.)

THE Noam PETERS gqlynorabwuu, wAsnmumnfu. c.

' UNITED STATES PATENT .FFICE.

ARTHUR C. EASTIVOOD, OF CLEVELAND, OHIO, ASSIGNOR TO THE ELECTRICCONTROLLER AND SUPPLY COMPANY, OF CLEVELAND, OHIO, A CORPO- RATION OFOHIO.

RH EOSTAT.

SPECIFICATION forming part of Letters Patent No. 704,448, dated July 8,1902.

Application filed April 10, 1902. Serial No. 102,234. (No model.) I

To a w/tmn it may concern:

Beit known that I, ARTHUR O. EASTWOOD, a citizen of the United States,and a resident of Cleveland, Ohio, have invented certain Im- 5provements in Rheostats, of which the following is a specification.

My invention consists of an improved form of electrical resistancedesigned for use in connection with electric controllers, speed-regu- 1olators, motor-starting boxes, field-regulating rheostats, dimmers,electrical heaters, and similar apparatus commonly employed for limitingor regulating the flow of an electric current by means of'ohmicresistance.

The object of my invention is to produce an electrical resistance orrheostat which is simple and economicalto manufacture and which Whilebeing of substantial construction is so made that its surface availablefor radiating 2o heatmay be indefinitelyincreased without undulymultiplying the number of parts.

A further object of the invention is to provide a rheostat having thecharacteristics above noted which shall be unaffected by heat andmoisture.

These objects I secure as hereinafter set forth, reference being had tothe accompanying drawings, in which- Figure l is an elevation of thepreferred form of my improved rheostat, the same being partly in sectionto show its interior construction. Fig. 2 is an end elevation of therheostat shown in Fig. 1, and Fig. 3 is a slightly-modified form of myinvention which is particularly adapted to continuously absorb anddissipate a relatively large amount of electrical energy.

In the above drawings, A is a metallic bar or rod having at one end ahead a and provided with threads at its other end for the accommodationof a nut ct. Upon this bar as a support is placed a tube of someinsulating material B, as fiber or porcelain, provided at its ends withwashers or rings I), also of insulating material. Carried upon this tubeB and between the end pieces Z) are a number of thin metallic plates and0, whose surfaces are coated with a thin film or sheet of an electricalconducting material of relatively high resistance. This sheet may beapplied chemically, electrochemically, mechanically,

or by a combination of these methods and is preferably in the form of abasic oxid of the metal upon whichitis deposited. Bya basic oxid ismeant one which will neither absorb oxygen nor give up oxygen, andwhileIpreferably employ such a compound it will be understood that I donot limit myself to the same, since I may, if desired, employ otherchemical compounds of the metal forming the plates 0 and c as well ascompounds of other metals. The particular metal which I have found togive the best results is sheet iron or steel in the form of thin plates,as noted, coated with a thin film or sheet of the oxid of iron havingthe chemical composition denoted by the symbols Fe O,.

It will be seen that the plates care of greater diameter than the plates0, extending beyond the edges of these latter, so as to expose aconsiderable surface of their area for the purpose of radiating heat andpermitting further circulation of air. I also preferably form thetwo'sets of plates with the holes through them of differentdiameters,,so that anybur formed in punching said plates may notinterfere with the contact between their surfaces.

As shown in the figures, there are plates 0 formed with a projectingarm, placed at intervals between the plates 0 and 0, these armsproviding for the attachment of wires from any desired form ofelectrical apparatus and being made either of the same metal as thatcomposing the plates 0 and c or of different metal. It is evident thatby varying the relative diameters of these latter two sets of plates theheat-radiating surface of the de vice may be adjusted to dissipate anyrequired amount of electrical energy.

Between the insulating end pieces I) and the head and nut of the rod A,I place angleshaped pieces of metal D, slotted, as shown at d, for thereception of a bolt or other device for retaining the rheostat inposition.

In order to provide for the longitudinal expansion of the rheostatcaused by its rise in temperature when in operation, I place aspring-washer E, of any well-known form, between the head or nut of thebolt and the angle-piece D. Under ordinary conditions the expansion ofthe various parts would have no material effect; but in my device unlessthere were some yielding member, as the spring-Washer, the pressurebetween the various plates of metal would be increased and theresistance of the rheostat thereby varied. By providing, however, theyielding member I am enabled to maintain the electrical resistance ofthe rheostat practicallyconstant irrespective of the expansion due tothe heat generated.

WVhen a considerable amount of electrical energy is to be dissipated foran extended period of time, I employ the form of device illustrated inFig. 3, in which the supporting parts of the device are the same as inFig. 1, while certain of the conducting members are made with aconsiderable mass of metal, as indicated at C, Fig. Here the plates 0are, as before, preferably of iron coated with a basic oxid, while theplates C are made of metal which is a good conductor of heatas, forinstance, c0pperthese being formed with a relatively large mass or bodyadjacent to that portion of their surface in contact with theintermediate plates 0 and having extended flanges or webs c projectingbeyond the said plates. These webs carry away the heat and dissipate it,as before, by radiation and conduction. Connection is made to the devicethrough the terminal pieces 0.

It will be noted that very little insulating material is required in theconstructions illus trated, these being simple and substantial and ofsuch design that by a very slight modification their resistance may bevaried to meet the various requirements of the different kinds of workin which rheostats are employed.

It will of course be understood that in operation the current passes inat the contact or terminal pieces and through the various plates 0 and0, meeting with resistance whenever it passes from plate to plate, owingto the comparatively low conductivity of the sheet of oxid coating thesurfaces of said plates. The heat generated at these points of contactis quickly dissipated by the relatively large heat-radiating surfacesformed by the outwardly-projecting portions of the alternate plates.

I claim as my invention 1. A. rheostat consisting of a series of platesof relatively high electrical conductivity having coatings of relativelylow conductivity, with means yieldingly holding said plates in contactwith one another, said plates being connected to each other through saidcoatings, substantially as described.

2. Arheostat consisting of a series of plates of relatively highelectrical conductivity having coatings of relatively low conductivity,certain of said plates extending beyond the 1 edges of others andthereby providing heat radiating surface, with means yieldingly holdingsaid plates in contact with one another, substantially as described.

3. Arheostat consistingof a series of plates of relatively highelectrical conductivity having coatings of relatively low conductivity,said plates having openings through them and having certain. of theirnumber extending beyond the others, a supporting member extendingthrough said openings having means for yieldingly retaining the platesin contact with one another, substantially as described.

a. In a rheostat, the combination of metal plates having their surfacescoated with a1naterial of relatively low electrical conductivity, bodiesof metal between said plates of relatively large mass, said bodieshaving portions thinner than the remainder thereof extended beyond saidplates, thereby providing heat-radiating surface, the plates and saidbodies of metal being electrically connected through the said coatings,substantially as described.

A rheostat consisting of a series of metallic plates, said plates havingupon their surfaces a coating of a material of relatively lowconductivity, and being electrically connected through said coatings,said plates having a relatively large body portion adjacent to theircontact-surfaces and having portions extending beyond said surfaces ofless thickness than said body portions, with plates of uniform thicknessalternating with said other plates, substantially as described.

6. Arheostat consisting of a series of plates having openings throughthem, a supporting member extending through said openings, certain ofsaid plates extending beyond the edges of others and certain of theopenings through the plates being of a size different from those throughthe others, substantially as described.

7. The combination in a rheostat of a series of metal plates ofrelatively great thickness at certain points, plates of substantiallyuniform thickness alternating with said other plates, said plates ofuniform thickness having a coating of relatively low electricalconductivity upon their surfaces, with means for retaining said platesin contact with one another, substantially as described.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

ARTHUR C. EASTWOOD.

\Vitnesses:

l VILLTAM E. Bnannnv, Jos. ll. KLEIN.

III

